feat: brand 白名单下发(站点覆盖/租户头像/CORS) + widget/chat 客户端 key 租户化 + 会话站点标

Co-Authored-By: Claude Code <noreply@anthropic.com>

seed_profiles/auto/tenant.json

@@ -13,7 +13,9 @@
       "title": "HESU Support",
       "color": "#f08a31",
       "whatsapp": "+8619037179250",
-      "email": "info@borderlesscar.com"
+      "email": "info@borderlesscar.com",
+      "welcome": "Hey! What kind of car are you looking for?",
+      "topics": ["Get Quotation", "Distributor Cooperation"]
     },
     "push": {
       "prefix": "ai-kefu"

seed_profiles/jiancai/tenant.json

@@ -22,7 +22,9 @@
       "color": "#066fc0",
       "whatsapp": "+8615937108317",
       "email": "hesu@hesuu.com",
-      "privacy_url": "https://hesupipe.com/privacy-policy"
+      "privacy_url": "https://hesupipe.com/privacy-policy",
+      "welcome": "What kind of piping project are you working on?",
+      "topics": ["Get Quotation", "Pipe Specifications", "Delivery & Shipping"]
     },
     "push": {
       "prefix": "ai-kefu-jc"